Electrolyte for electrolytic capacitor

ABSTRACT

An electrolyte having a high conductivity, an excellent high-temperature life characteristic and leading to improvement of the shelf characteristic of an aluminum electrolytic capacitor. At least one phosphate ion producing compound and a chelating agent are added using a solvent largely composed of water. Therefor, an aluminum electrolytic capacitor comprising such an electrolyte has a low impedance, an excellent high-temperature life characteristic, and an improved shelf characteristic.

INDUSTRIAL FIELD OF APPLICATION

The present invention relates to an electrolytic solution for anelectrolytic capacitor.

PRIOR ART

An aluminum electrolytic capacitor generally has the followingconstitution. Specifically, a high-purity aluminum foil shaped in astrip form is subjected to a surface-enlargement treatment by chemicalor electrochemical etching, and the aluminum foil whose surface has beensubjected to an enlargement treatment is subjected to a formationtreatment in a forming solution, such as an aqueous ammonium boratesolution, to prepare an anodic foil comprising the aluminum foil havingan oxide film layer formed thereon. Then, the anodic foil is overlappedand wound with a cathodic foil, which is prepared by subjecting ahigh-purity aluminum foil to a surface-enlargement treatment in asimilar manner, via a separator, to prepare a capacitor element. Thecapacitor element is then dipped in an electrolytic solution for drivingand housed in a metallic sheathed package in a closed-end cylindricalform. Further, a sealing member made of elastic rubber is inserted intoan open-end section of the sheathed package, and the open-end section ofthe sheathed package is sealed by drawing, whereby an aluminumelectrolytic capacitor is constituted.

As the electrolytic solution impregnated into the capacitor element of acompact aluminum electrolytic capacitor for low voltage, one havingethylene glycol as a main solvent and an ammonium salt of adipic acid,benzoic acid or the like as a solute, one having γ-butyrolactone as amain solvent and a quaternary cyclic amidinium salt of phthalic acid,maleic acid or the like as a solute, and the like have beenconventionally known.

Problems that the Invention is to Solve

Applications of the electrolytic capacitor include an electronicapparatus, such as an output smoothing circuit of a switching powersupply or the like. While low impedance characteristics are demanded inthese applications, such demand is being increased for an electrolyticcapacitor along with the progress of miniaturization of the electronicapparatus. The conventional electrolytic solution cannot deal with thedemand, and an electrolytic solution having a higher electroconductivityis demanded. The invention is to solve the problem, and one objectthereof is to provide an electrolytic solution for an electrolyticcapacitor that can realize a low impedance electrolytic capacitor, has ahigh electro-conductivity, and is excellent in high-temperature servicelife characteristics.

The conventional aluminum electrolytic capacitor has such problems that,upon allowing to stand, the capacitance is decreased, and the leakagecurrent characteristics are deteriorated, which finally cause opening ofa safety valve, and the reliability of the electrolytic capacitor isgreatly influenced by the shelf characteristics, which are thecharacteristics after lapsing a long period of time under load or underno load.

Accordingly, when an aluminum electrolytic capacitor that had beendeteriorated by allowing to stand for a long period of time wasanalyzed, it was found that the pH of the electrolytic solution isincreased, and an anionic component, i.e., the solute, was attached tothe surface of the electrode foil. It becomes apparent from these factsthat aluminum on the surface of the electrode foil is reacted with theanionic component as the solute to attach on the electrode foil, andaluminum is dissolved to form a hydroxide, part of which is reacted withthe anionic component as the solute to form a hydrogen gas through thereaction. The reaction is repeated to increase the pH, and finally itbrings about deterioration of the electrode foil and opening of thevalve.

Meanwhile, it has been well known that phosphoric acid is effective forprevention of the deterioration of an electrode foil, but it is notsufficient. This is because even when phosphoric acid is added, thephosphoric acid thus added is bonded to aluminum in the electrolyticsolution to form a water-insoluble complex, and the insoluble complex isattached to the electrode foil, whereby the phosphoric acid isdiminished from the electrolytic solution. Furthermore, when theaddition amount is too large, such a problem arises that the leakagecurrent is increased. However, the characteristics of the electrolyticcapacitor are maintained in good conditions during the period where thephosphate ions remain in an appropriate amount before diminishmentthereof, and therefore, the invention has been completed, another objectof which is to improve the shelf characteristics of the electrolyticcapacitor.

Means for Solving the Problems

The electrolytic solution for an aluminum electrolytic capacitor of theinvention is characterized by containing a solvent containing water anda water-soluble aluminum complex having a phosphate ion combinedthereto.

The water-soluble aluminum complex having a phosphate ion combinedthereto can be formed by adding a compound forming a phosphate ion in anaqueous solution (a phosphate ion forming compound) and a chelatingagent forming a water-soluble aluminum complex with aluminum. Thephosphate ion forming compound can be selected from the phosphoruscompounds described later, phosphoric acid, phosphorous acid,hypophosphorous acid, salts thereof, condensates thereof, and salts ofthe condensates.

In a preferred embodiment of the invention, at least one kind of adipicacid and a salt thereof is used as the solute.

The solvent contains water as a main component (i.e., in an amount ofabout 25% or more), and the content of water is generally from 35 to100% by weight of the entire solvent.

The content of adipic acid or a salt thereof is generally from 5 to 20%by weight of the entire electrolytic solution.

The content of the phosphorus compounds, phosphoric acid, phosphorousacid, hypophosphorous acid, salts thereof, condensates thereof, andsalts of the condensates is generally from 0.01 to 3.0% by weight of theentire electrolytic solution.

The content of the chelating agent is generally from 0.01 to 3.0% byweight of the entire electrolytic solution.

Mode for Carrying Out the Invention

The electrolytic solution for an aluminum electrolytic capacitor of theinvention is an electrolytic solution, in which the compound forming aphosphate ion in an aqueous solution and the chelating agent are addedto the solvent containing water to form a combined product of thewater-soluble aluminum complex and a phosphate ion, and after beingimpregnated in the capacitor element, it reacts with aluminum elutedfrom the aluminum foil used as the electrode foil to the electrolyticsolution, so as to form the combined product of the water-solublealuminum complex and a phosphate ion.

As the solvent, a protonic polar solvent, an aprotonic solvent and amixture thereof can be used in addition to water. Examples of theprotonic polar solvent include a monohydric alcohol (such as methanol,ethanol, propanol, butanol, hexanol, cyclohexanol, cyclopentanol, benzylalcohol and the like), a polyhydric alcohol and an oxyalcohol compound(such as ethylene glycol, propylene glycol, glycerin, methyl cellosolve,ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol and the like).Representative examples of the aprotic solvent include an amide series(such as N-methylformamide, N,N-dimethylformamide, N-ethylformamide,N,N-diethylformamide, N-methylacetamide, hexamethylphosphoric amide andthe like), a lactone compound, a cyclic amide compound, a carbonatecompound (such as γ-butyrolactone, N-methyl-2-pyrrolidone, ethylenecarbonate, propylene carbonate and the like), a nitrile compound (suchas acetonitrile and the like), an oxide compound (such as dimethylsulfoxide and the like) and the like.

As the compound forming a phosphate ion in an aqueous solution (thephosphate ion forming compound), the following compounds can beexemplified. They are the phosphorus compounds described later,phosphoric acid, phosphorous acid, hypophosphorous acid, salts thereof,condensates thereof, and salts of the condensates.

Examples of the above-described phosphorus compound and salt thereofinclude analkyl phosphate, such as ethyl phosphate, diethyl phosphate,butyl phosphate, dibutyl phosphate and the like; a phosphonate and adiphosphonate or a derivative thereof, such as phosphonic acid,1-hydroxyethylidene-1, 1-diphosphonic acid, aminotrimethylenephosophonicacid, phenylphosphonic acid and the like; a phosphinate, such as methylphosphinate, butyl phosphinate and the like; and salts of all of them.Among these, are preferred dibutyl phosphate,1-hydroxyethylidene-1,1-diphosphonic acid, and salts of them. As thesalts of the phosphorus compounds, an ammonium salt, an aluminum salt, asodium salt, a potassium salt, a calcium salt and the like can be used.

A condensed phosphoric acid, which is a condensate of phosphoric acid,and a salt thereof are used. As the condensed phosphoric acid, a linearcondensed phosphoric acid, such as pyrophosphoric acid,tripolyphosphoric acid, tetra-polyphosphoric acid and the like, a cycliccondensed phosphoric acid, such as metaphosphoric acid,hexametaphosphoric acid and the like, and a product formed by combiningthe linear and cyclic condensed phosphoric acids. As the salts of thecondensed phosphoric acid, an ammonium salt, an aluminum salt, a sodiumsalt, a calcium salt, a potassium salt and the like can be used. Amongthese, are preferred pyrophosphoric acid, tripolyphosphoric acid,tetrapolyphosphoric acid and salts of them, and are more preferredpyrophosphoric acid, tripolyphosphoric acid and salts of them, withtripolyphosphoric acid being most preferred. As the salts of thecondensates, an ammonium salt, an aluminum salt, a sodium salt, apotassium salt, a calcium salt and the like can be used.

Furthermore, as the phosphate ion forming compound, phosphoric acid,phosphorous acid, hypophosphorous acid and salts of them can be used.The salts thereof are an ammonium salt, an aluminum salt, a sodium salt,a calcium salt and a potassium salt. Phosphoric acid and a salt thereofform a phosphate ion through decomposition in an aqueous solution.Phosphorous acid, hypophosphorous acid and salts of them form aphosphite ion and a hypophosphite ion through decomposition in anaqueous solution, which then become phosphate ions through oxidation.

As the condensate other than the condensed phosphoric acid, thephosphorus compounds, phosphorous acid, hypophosphorous acid, salts ofthem, and condensates of the phosphorus compounds, phosphorous acid,hypophosphorous acid and a salt of hypophosphorous acid can be used.Furthermore, salts of the condensates can also be used. As the salts ofthe condensates, an ammonium salt, an aluminum salt, a sodium salt, apotassium salt, a calcium salt and the like can be used.

These are also the phosphate ion forming compounds, which form aphosphate ion in an aqueous solution or form a phosphite ion or ahypophosphite ion, which then become a phosphate ion through oxidation.

Among these, phosphoric acid or a salt thereof, condensed phosphoricacid, and a derivative of phosphoric acid, such as a phosphate or analkyl phosphate, which easily form a phosphate ion, are preferred.Further, a linear condensed phosphoric acid. Such as phosphoric acid,pyrophosphoric acid, tri-polyphosophoric acid or the like, which forms alarge amount of phosphate ions in a relatively high rate with respect tothe addition amount, and a salt thereof are also preferred. In additionto these phosphate ion forming compounds, the effect of the inventioncan be obtained by substances that form a phosphate ion in an aqueoussolution.

The addition amount of the phosphate ion forming compound is from 0.01to 3.0% by weight, and preferably from 0.2 to 2.0% by weight, of theentire electrolytic solution. The effect is reduced outside the range.

Similarly, the chelating agent forming a water-soluble aluminum complexwith aluminum is used as an additive. As the chelating agent, thefollowing can be exemplified. That is, they are an α-hydroxycaboxylicacid, such as citric acid, tartaric acid, gluconic acid, malic acid,lactic acid, glycolic acid, α-hydroxybutylic acid, hydroxymalonic acid,α-methylmalic acid, dihydroxytartaric acid and the like, an aromatichydroxycarboxylic acid, such as γ-resocylic acid, β-resocylic acid,trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid,phenoltricarboxylic acid, aluminon, Eriochrome Cyanine R and the like, asulfocarboxylic acid, such as sulfosalicylic acid and the like, atannin, such as tannic acid and the like, a guanidine, such asdicyandiamide and the like, a saccharide, such as galactose, glucose andthe like, a lignin, such as lignosulfonate and the like, anaminopolycarboxylic acid, such as ethylenediaminetetraacetic acid(EDTA), nitrilotriacetic acid (NTA), glycolether-diaminetetraacetic acid(GEDTA), diethylenetriamine-pentaacetic acid (DTPA),hydroxyethylethylenediamine-triacetic acid (HEDTA),triethylenetetraminehexaacetic acid (TTHA) and the like, and salts ofthem. As the salts of them, an ammonium salt, an aluminum salt, a sodiumsalt, a potassium salt and the like can be used. Among these, arepreferred tannic acid, trihydroxybenzoic acid, citric acid, tartaricacid, gluconic acid, aurin tricarboxylic acid, γresocylic acid, DTPA,EDTA, GEDTA, HEDTA, TTHA and salts thereof, which easily exert chelateformation with aluminum, and are more preferred tannic acid,trihydroxybenzoic acid, citric acid, tartaric acid, γ-resocylic acid,aurin tricarboxylic acid, DTPA, GEDTA, HEDTA, TTHA and salts thereof.

The addition amount of the chelating agent is from 0.01 to 3.0% byweight, and preferably from 0.1 to 2.0% by weight, of the entireelectrolytic solution. The effect is reduced outside the range.

As the solute of the electrolytic solution for an aluminum electrolyticcapacitor used in the invention, an ammonium salt, a quaternary ammoniumsalt or an amine salt of a carboxylic acid, such as adipic acid, formicacid, benzoic acid and the like, can be used. Examples of a quaternaryammonium constituting the quaternary ammonium salt include atetraalkylammonium (such as tetramethylammonium, tetraethylammonium,tetrapropyl-ammonium, tetrabutylammonium, methyltriethylammonium,di-methyldiethylammonium and the like) and a pyridinium (such as1-methylpyridinium, 1-ethylpyridinium, 1,3-diethylpyridinium and thelike). Examples of an amine constituting the amine salt include aprimary amine (such as methylamine, ethylamine, propylamine, butylamine,ethylenediamine, monoethanolamine and the like), a secondary amine (suchas dimethylamine, diethylamine, dipropylamine, ethylmethylamine,diphenylamine, diethanolamine and the like), and a tertiary amine (suchas trimethylamine, triethylamine, tributylamine,1,8-diazabicyclo(5,4,0)-undecene, 7-triethanolamine and the like).

Furthermore, the following acids can be used as the carboxylic acid.They are carboxylic acids including glutaric acid, succinic acid,isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluicacid, enanthic acid, malonic acid, a decanedicarboxylic acid, such as1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid and the like,an octanedicarboxylic acid, such as 1,7-octane-dicarboxylic acid and thelike, azelaic acid, sebacic acid and the like. An inorganic acid, suchas boric acid, a polyhydric alcohol complex compound of boric acidobtained from boric acid and a polyhydric alcohol, phosphoric acid,carbonic acid, silicic acid and the like, can also be used. Among them,are preferred an organic carboxylic acid, such as a decanedicarboxylicacid, an octanedicarboxylic acid, azelaic acid, sebacic acid, adipicacid, glutaric acid, succinic acid, benzoic acid, isophthalic acid,formic acid and the like, boric acid and a polyhydric alcohol complexcompound of boric acid.

A salt having a quaternary cyclic amidinium ion as a cationic componentmay also be used. Examples of an acid forming an anionic component ofthe salt include phthalic acid, isophthalic acid, terephthalic acid,maleic acid, benzoic acid, toluic acid, enanthic acid, malonic acid andthe like.

The quaternary cyclic amidinium ion as a cationic component is a cationformed by quaternarizing a cyclic compound having an N,N,N′-substitutedamidine group, and the following compounds are exemplified as the cycliccompound having an N,N,N′-substituted amidine group. They are animidazole monocyclic compound (for example, an imidazole homologue, suchas 1-methylimidazole, 1-phenylimidazole, 1,2-dimethyl-imidazole,1-ethyl-2-methylimidazole, 1,2,4-trimethylimidazole and the like, anoxyalkyl derivative, such as 1-methyl-2-oxymethylimidazole,1-methyl-2-oxyethyl-imidazole and the like, a nitro derivative such as1-methyl-4(5)-nitroimidazole and the like, an amino derivative such as1,2-dimethyl-5(4)-aminoimidazole and the like), a benzoimidazolecompound (such as 1-methylbenzoimidazole, 1-methyl-2-benzoimidazole,1-methyl-5(6)-nitrobenzo-imidazole and the like), a compound having a2-imidazoline ring (such as 1-methylimidazoline,1,2-dimethylimidazoline, 1,2,4-trimethylimidazoline,1-methyl-2-phenylimidazoline, 1-ethyl-2-methylimidazoline,1,4-dimethyl-2-ethyl-imidazoline, 1-methyl-2-ethoxymethylimidazoline andthe like), a compound having a tetrahydropyrimidine ring (such as1-methyl-1,4,5,6-tetrahydropyrimidine,1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1,5-diazabicyclo[4,3,0]nonene-5 and the like), and the like.

The aluminum electrolytic capacitor containing the electrolytic solutionfor an aluminum electrolytic capacitor of the invention described in theforegoing is good in shelf characteristics, i.e., characteristics aftera load or no load test for a long period of time, and further theinitial capacitance is also increased.

After impregnating a capacitor element with the electrolytic solutionfor an aluminum electrolytic capacitor of the invention, the chelatingagent forms a water-soluble complex with aluminum eluted from thealuminum foil in the electrolytic solution, which forms a combinedproduct through a reaction with a phosphate ion. The combined product isattached to the electrode foil or is dissolved in the electrolyticsolution and releases phosphate ions in that state, so as to exert suchfunction that phosphate ions in the electrolytic solution are maintainedin a suitable amount. The phosphate ions suppress dissolution ofaluminum and formation of a hydroxide of aluminum to suppressdeterioration of the electrode foil, whereby the shelf characteristicsof the aluminum electrolytic capacitor are improved. The phosphate ionsin the electrolytic solution and the phosphate ions in the combinedproduct are detected for a long period of time after allowing to standin an amount of from 10 to 40,000 ppm in terms of a phosphate radical(the electrolytic solution is diluted with diluted nitric acid of 2mmol/L to 1,000 times to make pH of from 2 to 3, and phosphate ions arequantitatively determined by an ionic chromatography analysis).

The following experiments clarify these facts. The aluminum electrolyticcapacitor of the invention was disassembled, and the electrolyticsolution impregnated in the capacitor element was washed and removed.Thereafter, the capacitor element was impregnated with an electrolyticsolution containing no phosphate ion to produce an aluminum electrolyticcapacitor, and the shelf characteristics of the resulting aluminumelectrolytic capacitor were excellent. Phosphate radicals of from 10 to200 ppm were detected from the electrolytic solution of the aluminumelectrolytic capacitor, but substantially no aluminum was detected. Thatis, the water-soluble complex of the chelating agent and aluminum iscombined to phosphate ions to be attached to the electrode foil, and thecombined product releases phosphate ions into the electrolytic solutionto maintain the suitable phosphate ion concentration for a long periodof time, whereby the shelf characteristics of the capacitor areimproved.

In the case where the aluminum complex thus formed is not water-soluble,i.e., water-insoluble, the effect of the invention cannot be obtainedbecause it is considered that it has no function of releasing phosphateions.

In general, when the content of water in the solvent is increased, thepresure inside the capacitor is increased due to formation of a hydrogengas, causing such situation that blister is formed on the package.Particularly, in a high-temperature service life test at 105° C. orhigher, when the content of water exceeds 15% by weight, a large amountof gas is formed to increase the pressure inside the capacitor to causesuch a situation that the safety valve is opened, and thus, it becomesunusable. That is, the state where the cathodic foil is in contact withthe electrolytic solution at a high temperature is continued for a longperiod of time, and under the presence of a large amount of water, waterreaches the aluminum foil through the dense oxide film formed on thealuminum film and reacts with aluminum to form aluminum hydroxide. Ahydrogen gas is formed at this time. Furthermore, the reaction suddenlyproceeds at a high temperature of 105° C. or higher to form a largeamount of gas, and thus, it results in an increase of the inner pressureof the capacitor and opening of the valve of the capacitor.

However, in the electrolytic solution for an aluminum electrolyticcapacitor of the invention, because the phosphate ion forming compoundand the chelating agent are added to the solvent containing water as amain component as an electrolytic solution, the specific resistance ofthe electrolytic solution can be reduced, and the impedance of theelectrolytic capacitor can be reduced. Furthermore, because thephosphate ion concentration of the electrolytic solution in thecapacitor element can be maintained to a suitable amount for a longperiod of time by the chelating agent, dissolution and deterioration ofthe electrode foil can be prevented, and the high-temperature servicelife characteristics of the aluminum electrolytic capacitor can bemaintained in an excellent state.

The chelating agent and the phosphate ion forming compound added uponproducing the electrolytic solution provide the chelating agent and aphosphate ion in the electrolytic solution of a molar ratio, chelatingagent/phosphate ion, of from {fraction (1/20)} to {fraction (3/1)}.Furthermore, it is preferably from {fraction (1/10)} to {fraction(1/1)}. When the amount of the chelating agent is smaller than theratio, the leakage current characteristics of the aluminum electrolyticcapacitor are lowered. When it is more than the ratio, thehigh-temperature service life characteristics of the aluminumelectrolytic capacitor are deteriorated although the reasons thereforare not clear.

When a large amount of water is contained in the electrolytic solution,deterioration of the electrode foil becomes remarkable, and inparticular, when the content of water in the electrolytic solutionexceeds 15%, such problem occurs that deterioration of thecharacteristics of the aluminum electrolytic capacitor becomesremarkable under the conditions for allowing to stand of 125° C. orhigher. In the invention, however, it has been found that the effect isobtained even in the case where a large amount of water is contained,and thus, an aluminum electrolytic capacitor having low impedancecharacteristics can be obtained by using the electrolytic solution.

That is, an aluminum electrolytic capacitor having low impedancecharacteristics can be realized by using a solvent containing water as amain component in the electrolytic solution for a aluminum electrolyticcapacitor of the invention.

The content of water is generally from30 to 100% by weight, preferablyfrom 35 to 65% by weight, and more preferably from 55 to 65% by weight,of the entire solvent. The electro-conductivity is lowered outside therange.

As described in the foregoing, in the electrolytic solution for analuminum electrolytic capacitor of the invention, even when the contentof water is 15% by weight or more, an aluminum electrolytic capacitorhaving excellent high-temperature service life characteristics andwithstanding a high-temperature test of 105° C. or higher can beobtained. Furthermore, because the content of water in the solvent canbe increased to 100% by weight to obtain an electrolytic solutioncontaining water as a main component, the electroconductivity of theelectrolytic solution can be increased to obtain an aluminumelectrolytic capacitor having low impedance characteristics.

Furthermore, it can be used at 125° C. when the content of water is 65%by weight or more. Therefore, the range where it has a highelectroconductivity and can be used at 125° C. is from 55 to 65% byweight. In the case where the phosphate ion forming compound and thechelating agent, which are used as additives in the invention, are usedsingly within the range of the content of water of 65% by weight orlower, there are some cases where it withstands the service life test at105° C., but it suffers from opening of the valve in the initial stageon the high-temperature service life test of 125° C. or higher. However,it can be used at 125° C. owing to the synergistic effect between thephosphate ion forming compound and the chelating agent.

Furthermore, in the conventional aluminum electrolytic capacitor usingan electrolytic solution containing water, the leakage current isincreased after a high-temperature no load test, but in the aluminumelectrolytic capacitor using the electrolytic solution for an aluminumelectrolytic capacitor of the invention, the increase of the leakagecurrent is small, and the change of tan δ after the high-temperaturetest is smaller than the conventional product, whereby thehigh-temperature service life characteristics are improved.

As described in the foregoing, the content of water in the solvent canbe increased to 100% by weight by adding the phosphate ion formingcompound and the chelating agent to the solvent containing water as amain component, whereby an electrolytic solution having a highelectroconductivity can be obtained, blister and opening of the valve inthe package of the capacitor are prevented, and the tan δ and theleakage current characteristics after the high-temperature test areimproved. Accordingly, the invention realizes an electrolytic capacitorhaving impedance characteristics and high-temperature service lifecharacteristics, which cannot be found in the conventional art, owing tothe synergistic effect among the solvent containing water as a maincomponent, the phosphate ion forming compound and the chelating agent.

The electrolytic solution for an aluminum electrolytic capacitor of theinvention using the solvent containing water as a main component doesnot suffer from such problem as ignition even in the case where thecapacitor is broken down upon using under non-standard conditions, suchas use at high voltage. Other components than the solvent are thephosphoric, acid forming compound and the chelating agent, and thereforethe components constituting the electrolyte have high safety. It is thusexcellent in environmental resistance.

The impedance is further decreased by using at least one kind of adipicacid and a salt thereof as the solute.

The content of adipic acid or a salt thereof is from 5 to 20% by weight,and preferably from 9 to 16% by weight, in the electrolytic solution.The electroconductivity is decreased when it is less than the range, andthe solubility is decreased when it exceeds the range. The content ofother solute is also about from 5 to 20% by weight, and preferably aboutfrom 9 to 16% by weight, in the entire electrolytic solution.

Furthermore, an improvement of the voltage resistance can be attained byadding boric acid, mannitol, a nonionic surfactant, colloidal silica andthe like to the electrolytic solution for an electrolytic capacitor ofthe invention.

By using the electrolytic solution for an aluminum electrolyticcapacitor of the invention, such aluminum electrolytic capacitor can beobtained that is excellent in impedance characteristics and further, inhigh-temperature service life characteristics.

The invention will be described more specifically below with referenceto the Examples.

EXAMPLES

The invention will be described in detail with reference to FirstExample. The capacitor element is formed by rolling up an anodic foiland a cathodic foil with a separator intervening therebetween. Theanodic foil used is one obtained in such a manner that an aluminum foilof a purity of 99.9% is subjected to chemical or electrochemical etchingin an acidic solution to enhance the surface area thereof and thensubjected to a chemical treatment in an ammonium adipate aqueoussolution, so as to form an anodic oxide film layer on the surfacethereof. The cathodic foil used is an aluminum foil of a purity of 99.9%having been subjected to etching to enhance the surface area thereof.

The capacitor element thus constituted in the foregoing manner isimpregnated with an electrolytic solution for driving an electrolyticcapacitor. The capacitor element impregnated with the electrolyticsolution is housed in an aluminum cylindrical outer package with abottom, a sealing member formed with butyl rubber is inserted into anopen end of the outer package, and further, the open end of the outerpackage is sealed by drawing to seal the aluminum electrolyticcapacitor.

The compositions and the characteristics of the electrolytic solutionsused herein are shown in Tables 1-1 and 1-2.

The aluminum electrolytic capacitors thus constituted were subjected toa high-temperature service life test. The rating of the aluminumelectrolytic capacitors is 50 WV-100 μF. The test conditions are at 125°C. with load of the rated voltage for 1,000 hours, and at 125° C. withno load for 1,000 hours for Examples 1-1 to 1-11, Conventional Example1-1, and Comparative Examples 1-1 and 1-2, and at 105° C. with load ofthe rated voltage for 1,000 hours, and at 105° C. with no load for 1,000hours for Examples 1-2 and 1-3, Conventional Example 1-2, andComparative Example 1-3, with the respective results being shown inTables 1-3 to 1-6 and Tables 1-7 and 1-8.

TABLE 1-1 Specific resistance Water EG AAd TRPA ACTR (Ωcm) Example 1-130(35) 56 12.0 1.0 1.0 89 Example 1-2 47(55) 39 12.0 1.0 1.0 42 Example1-3 52(60) 34 12.8 0.2 1.0 31 Example 1-4 52(60) 34 12.9 1.0 0.1 31Example 1-5 53(60) 36 9.0 1.0 1.0 39 Example 1-6 52(60) 34 12.0 1.0 1.032 Example 1-7 49(60) 33 16.0 1.0 1.0 30 Example 1-8 52(60) 34 11.0 1.02.0 33 Example 1-9 52(60) 34 11.0 2.0 1.0 33 (Note) EG: Ethylene glycolAAd: Ammonium adipate TRPA: Tripolyphosphoric acid ACTR: Ammoniumcitrate The parenthetic numerals in the column for water are thecontents of water in the solvent.

TABLE 1-2 Specific resistance Water EG AAd PRPA TRPA ACTR AGLC (Ωcm)Example 1-10 52(60) 34 12.0 — 1.0 — 1.0 31 Example 1-11 52(60) 34 12.01.0 — 1.0 — 32 Example 1-12 65(75) 21 12.0 — 1.0 1.0 — 24 Example 1-13 86(100) — 12.0 — 1.0 1.0 — 16 Conventional Example 1-1 5(5) 93 7.0 — —— — 248 Conventional Example 1-2  9(10) 77 14 — — — — 172 ComparativeExample 1-1  9(10) 77 13.0 — — 1.0 — 175 Comparative Example 1-2  9(10)77 13.0 — 1.0 — — 173 Comparative Example 1-3 13(15) 73 14 — — — — 129(Note) PRPA: Pyrophosphoric acid AGLC: Ammonium gluconate Theparenthetic numerals in the column for water are the contents of waterin the solvent.

TABLE 1-3 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-1 102 0.030 2.13 −6.1 0.096 1.49 Example 1−2103 0.020 1.88 −6.2 0.032 1.45 Example 1−3 103 0.020 1.93 −6.3 0.0301.46 Example 1−4 103 0.020 1.90 −6.2 0.029 1.56 Example 1−5 103 0.0201.99 −6.6 0.032 1.51 Example 1−6 103 0.019 1.93 −6.4 0.029 1.54 Example1−7 103 0.019 1.92 −6.3 0.030 1.52 (Note) Cap: Capacitance (μF) tan δ:Tangent of dielectric loss LC: Leakage current (μA) ΔCap: Change rate ofcapacitance (%)

TABLE 1-4 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-8  103 0.020 1.91 −6.3 0.027 1.40 Example1-9  103 0.020 1.90 −6.2 0.030 1.40 Example 1-10 103 0.020 1.93 −6.50.029 1.44 Example 1-11 103 0.019 1.93 −6.2 0.028 1.54 Conventional 1010.063 2.03 −7.3 0.232 1.54 Example 1-1 Comparative 102 0.043 1.90 Valveopened Example 1-1 Comparative 102 0.044 1.88 Valve opened Example 1-2

TABLE 1-5 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-1 102 0.029 2.13 −8.5 0.128 13.0 Example 1-2103 0.020 2.00 −7.9 0.027 12.0 Example 1-3 103 0.020 1.90 −7.2 0.02915.3 Example 1-4 104 0.019 2.03 −7.1 0.028 15.5 Example 1-5 103 0.0201.98 −8.1 0.029 14.8 Example 1-6 103 0.020 2.04 −7.2 0.026 15.0 Example1-7 103 0.019 1.91 −8.2 0.027 15.3

TABLE 1-6 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-8  104 0.021 2.00 −7.3 0.030 13.0 Example1-9  103 0.019 2.00 −7.3 0.028 14.5 Example 1-10 103 0.020 1.86 −7.40.029 12.3 Example 1-11 103 0.020 1.90 −7.2 0.028 12.0 Conventional 1010.065 2.22 −8.8 0.313 103 Example 1-1 Comparative 101 0.045 1.99 Valveopened Example 1-1 Comparative 101 0.044 2.03 Valve opened Example 1-1

TABLE 1-7 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-12 104 0.019 2.05 −4.8 0.021 1.59 ExampIe1-13 103 0.017 1.98 −4.8 0.022 1.5O Conventional 103 0.045 1.89 −4.20.063 1.59 Example 1-2 Comparative 103 0.038 1.92 Valve opened Example1-3

TABLE 1-8 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 1-12 103 0.018 2.05 −6.1 0.021 14.1 Example1-13 103 0.016 1.95 −6.1 0.021 14.7 Conventional 103 0.045 1.88 −5.10.069 85.1 Example 1-2 Comparative 104 0.037 1.91 Valve opened Example1-3

It is clear from Tables 1-1 to 1-8 that, in Examples 1-1 to 1-13 havingcontents of water in the solvent of from 35 to 100% by weight, theelectrolytic solution has a low specific resistance and a low tan δ inthe initial stage in comparison to the Conventional Examples. The changeof tan δ after the high-temperature test is also small. Furthermore, theleakage current after the high-temperature no load test is remarkablysmall in comparison to the Conventional Examples. In the results of thehigh-temperature test at 105° C. shown in Tables 1-7 and 1-8, goodresults are obtained in Examples 1-12 and 1-13 having high contents ofwater of from 75 to 100% by weight, whereas Comparative Example 1-3 notusing the condensed phosphoric acid and the chelating agent suffers fromopening of the valve even in the test period of several tens of hoursregardless of the low content of water of 15% by weight, and thus theeffect of the condensed phosphoric acid and the chelating agent in theinvention is understood. Furthermore, in the high-temperature test at125° C. shown in Tables 1-3 to 1-6, good results are obtained inExamples 1-1 to 1-11 having contents of water of from 35 to 60% byweight, whereas in Comparative Examples 1-1 and 1-2 using one of thecondensed phosphoric acid or the chelating agent singly, they sufferfrom opening of the valve even in the test period of several tens ofhours regardless of the low content of water of 10% by weight, and thus,the strong synergistic effect between the condensed phosphoric acid andthe chelating agent in the invention is understood.

The equivalent initial characteristics and service life characteristicsare obtained in Examples 1-5, 1-6 and 1-7 having contents of ammoniumadipate of 9.0, 12.0 and 14.0% by weight, Examples 1-3, 1-6 and 1-9having contents of tripolyphosphoric acid of 0.2, 1.0 and 2.0% byweight, and Examples 1-4, 1-6 and 1-8 having contents of ammoniumcitrate of 0.1, 1.0 and 2.0% by weight, and thus, it is understood thatexcellent characteristics are obtained within the ranges.

The invention will be described in detail with reference to SecondExample. Electrolytic capacitors were produced in the same manner as inthe First Example.

The compositions and the characteristics of the electrolytic solutionsused herein are shown in Tables 2-1 and 2-2.

The aluminum electrolytic capacitors thus constituted were subjected toa high-temperature service life test. The rating of the aluminumelectrolytic capacitors is 50 WV-100 μF. The test conditions are at 125°C. with load of the rated voltage for 1,000 hours, and at 125° C. withno load for 1,000 hours for Examples 2-1 to 2-11, Conventional Example2-1, and Comparative Examples 2-1 and 2-2, and at 105° C. with load ofthe rated voltage for 1,000 hours, and at 105° C. with no load for 1,000hours for Examples 2-12 and 2-13, Conventional Example 2-2, andComparative Example 2-3, with the respective results being shown inTables 2-3 to 2-6 and Tables 2-7 and 2-8.

TABLE 2-1 Specific resistance Water EG AAd TRPA ACTR (Ωcm) Example 2-130(35) 56 12.0 1.0 1.0 88 Example 2-2 47(55) 39 12.0 1.0 1.0 43 Example2-3 52(60) 34 12.8 0.2 1.0 31 Example 2-4 52(60) 34 12.9 1.0 0.1 31Example 2-5 53(60) 36 9.0 1.0 1.0 39 Example 2-6 52(60) 34 12.0 1.0 1.031 Example 2-7 49(60) 33 16.0 1.0 1.0 30 Example 2-8 52(60) 34 11.0 1.02.0 33 Example 2-9 52(60) 34 11.0 2.0 1.0 33 (Note) EC: Ethylene glycolAAd: Ammonium adipate DBP: Dibutyl phosphate ACTR: Ammonium citrate Theparenthetic numerals in the column for water are the contents of waterin the solvent.

TABLE 2-2 Specific resistance Water EG AAd DBP HEDP ACTR AGLC (Ωcm)Example 2-10 52(60) 34 12.0 — 1.0 — 1.0 32 Example 2-11 52(60) 34 12.01.0 — 1.0 — 31 Example 2-12 65(75) 21 12.0 — 1.0 1.0 − 23 Example 2-13 86(100) — 12.0 — 1.0 1.0 — 15 Conventional Example 2-1 5(5) 93 7.0 — —— — 248 Conventional Example 2-2  9(10) 77 14 — — — — 172 ComparativeExample 2-1  9(10) 77 13.0 — — 1.0 — 175 Comparative Example 2-2  9(10)77 13.0 — 1.0 — — 173 Comparative Example 2-3 13(15) 73 14 — — — — 129(Note) HEDP: 1-Hydroxyethylidene-1,1-diphosphoric acid AGLC: Ammoniumgluconate The parenthetic numerals in the column for water are thecontents of water in the solvent.

TABLE 2-3 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-1 103 0.029 2.11 −6.1 0.094 1.45 Example 2-2103 0.020 1.79 −6.2 0.031 1.48 Example 2-3 102 0.021 1.88 −6.2 0.0291.42 Example 2-4 103 0.021 1.89 −6.3 0.030 1.49 Example 2-5 103 0.0201.95 −6.5 0.031 1.53 Example 2-6 102 0.019 1.92 −6.3 0.030 1.51 Example2-7 103 0.020 1.91 −6.4 0.029 1.49 (Note) Cap: Capacitance (μF) tan δ:Tangent of dielectric loss LC: Leakage current (μA) ΔCap: Change rate ofcapacitance (%)

TABLE 2-4 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-8  102 0.019 1.90 −6.2 0.026 1.39 Example2-9  103 0.020 1.91 −6.1 0.029 1.41 Example 2-10 103 0.021 1.92 −6.40.030 1.42 Example 2-11 102 0.019 1.94 −6.3 0.029 1.53 Conventional 1010.063 2.03 −7.3 0.232 1.54 Example 2-1 Comparative 102 0.043 1.90 Valveopened Example 2-1 Comparative 102 0.044 1.88 Valve opened Example 2-2

TABLE 2-5 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-1 103 0.030 2.09 −8.3 0.125 13.3 Example 2-2103 0.021 2.03 −7.7 0.028 12.2 Example 2-3 102 0.019 1.92 −7.1 0.03015.1 Example 2-4 104 0.020 2.02 −7.2 0.027 15.8 Example 2-5 103 0.0201.95 −8.3 0.028 14.5 Example 2-6 102 0.019 2.03 −7.3 0.025 15.2 Example2-7 103 0.020 1.89 −8.1 0.028 15.1

TABLE 2-6 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-8  103 0.020 2.03 −7.2 0.029 13.2 Example2-9  103 0.018 2.09 −7.1 0.027 14.3 Example 2-10 104 0.021 1.91 −7.30.028 12.5 Example 2-11 103 0.020 1.88 −7.3 0.029 12.2 Conventional 1010.065 2.22 −8.8 0.313 103 Example 2-1 Comparative 101 0.045 1.99 Valveopened Example 2-1 Comparative 101 0.044 2.03 Valve opened Example 2-2

TABLE 2-7 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-12 103 0.020 2.09 −4.7 0.022 1.55 Example2-13 104 0.018 1.95 −4.9 0.021 1.51 Conventional 103 0.045 1.89 −4.20.063 1.59 Example 2-2 Comparative 103 0.038 1.92 Valve opened Example2-3

TABLE 2-8 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 2-12 102 0.018 2.03 −6.2 0.020 14.3 Example2-13 103 0.017 1.92 −6.0 0.020 14.5 Conventional 103 0.045 1.88 −5.10.069 85.1 Example 2-2 Comparative 104 0.037 1.91 Valve opened Example2-3

It is clear from Tables 2-1 to 2-8 that, in Examples 2-1 to 2-13 havingcontents of water in the solvent of from 35 to 100% by weight, theelectrolytic solution has a low specific resistance and a low tan δ inthe initial stage in comparison to the Conventional Examples. The changeof tan δ after the high-temperature test is also small. Furthermore, theleakage current after the high-temperature no load test is remarkablysmall in comparison to the Conventional Examples. In the results of thehigh-temperature test at 105° C. shown in Tables 2-7 and 2-8, goodresults are obtained in Examples 2-12 and 2-13 having high contents ofwater of from 75 to 100% by weight, whereas Comparative Example 2-3 notusing the phosphorus compound and the chelating agent suffers fromopening of the valve even in the test period of several tens of hoursregardless of the low content of water of 15% by weight, and thus, theeffect of the phosphorus compound and the chelating agent in theinvention is understood. Furthermore, in the high-temperature test at125° C. shown in Tables 2-3 to 2-6, good results are obtained inExamples 2-1 to 2-11 having contents of water of from 35 to 60% byweight, whereas in Comparative Examples 2-1 and 2-2 using one of thephosphorus compound or the chelating agent singly, they suffer fromopening of the valve even in the test period of several tens of hoursregardless of the low content of water of 10% by weight, and thus, thestrong synergistic effect between the phosphorus compound and thechelating agent in the invention is understood.

The equivalent initial characteristics and service life characteristicsare obtained in Examples 2-5, 2-6 and 2-7 having contents of ammoniumadipate of 9.0, 12.0 and 14.0% by weight, Examples 2-3, 2-6 and 2-9having contents of dibutyl phosphate of 0.2, 1.0 and 2.0% by weight, andExamples 2-4, 2-6 and 2-8 having contents of ammonium citrate of 0.1,1.0 and 2.0% by weight, and thus, it is understood that excellentcharacteristics are obtained within the ranges.

The invention will be described in detail with reference to ThirdExample. Electrolytic capacitors were produced in the same manner as inthe First Example.

The compositions of the electrolytic solutions used herein were 52 partsof water, 34 parts of ethylene glycol and 14 parts of ammonium adipate,to which the additives shown in Table 3-1 were added. As ComparativeExample 3-3, an electrolytic solution having 26 parts of water, 60 partsof ethylene glycol and 14 parts of ammonium adipate and containing noadditive was produced. Table 3-1 also shows the specific resistancethereof.

The aluminum electrolytic capacitors thus constituted were subjected toa service life test. The rating of the aluminum electrolytic capacitorsis 6.3 WV-5,600 μF. The test conditions are at 105° C. with load of therated voltage or no load for 1,000 hours. As for Examples 3-1, 3-2 and3-7, it was also carried out at 125° C. with load of the rated voltageor no load for 1,000 hours. The electric characteristics after the testare shown in Tables 3-2 to 3-5.

TABLE 3-1 Specific resistance DTPA GEDTA TTHA TaA GaA PRPA DBP 2PA (Ωcm)Example 3-1 1 — — — — 1 — — 28 Example 3-2 1 — — — — — 2 — 31 Example3-3 — 1 — — — 1 — — 28 Example 3-4 — — 1 — — 1 — — 29 Example 3-5 — — —1 — 1 — — 28 Example 3-6 — — — — 1 1 — — 29 Example 3-7 1 — — — — — — 128 Example 3-8 — 1 — — — — — 1 29 Example 3-9 — — 1 — — — — 1 29Comparative Example 3-1 — — — — — — —    0.005 26 Comparative Example3-2 — — — — — — — 1 27 Comparative Example 3-3 — — — — — — — — 80 (Note)DTPA: Diethylenetriaminepentaacetic acid GEDTA:Glycoletherdiaminetetraacetic acid TTHA: Triethylenetetraminehexaaceticacid TaA: Tannic acid GaA: 3,4,5- Trihydroxybenzoic acid (gallic acid)PRPA: Pyrophosphoric acid DBP: Dibutyl phosphate 2AP: Diammoniumhydrogenphosphate

TABLE 3-2 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 3-1 5,710 0.060 17 −11 0.071 14 Example 3-25,690 0.060 15 −11 0.070 16 Example 3-3 5,680 0.061 18 −10 0.070 15Example 3-4 5,650 0.060 19 −11 0.069 14 Example 3-5 5,680 0.061 15 −100.070 16 Example 3-6 5,680 0.060 16 −11 0.071 14 Example 3-7 5,700 0.06016 −10 0.070 15 Example 3-8 5,680 0.061 15 −10 0.069 12 Example 3-95,640 0.059 18 −12 0.073 16 Comparative 5,600 0.060 15 Valve openedExample 3-1 Comparative 5,610 0.061 35 Valve opened Example 3-2Comparative 5,610 0.109 14 Valve opened Example 3-3 (Note) Cap:Capacitance (μF) tan δ: Tangent of dielectric loss LC: Leakage current(μA) ΔCap: Change rate of capacitance (%)

TABLE 3-3 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 3-1 5,700 0.060 16 12 0.072 36 Example 3-25,700 0.061 14 −12 0.074 39 Example 3-3 5,680 0.060 18 −11 0.071 240Example 3-4 5,640 0.059 18 −10 0.069 318 Example 3-5 5,690 0.061 15 −100.070 29 Example 3-6 5,680 0.061 17 −11 0.071 28 Exampe 3-7 5,710 0.06015 −12 0.071 31 Example 3-8 5,680 0.061 13 −11 0.070 195 Example 3-95,640 0.059 18 −11 0.071 221 Comparative 5,600 0.060 12 Valve openedExampe 3-1 Comparative 5,600 0.061 42 Valve opened Example 3-2Comparative 5,600 0.110 16 Valve opened Example 3-3

TABLE 3-4 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 3-1 5,700 0.062 18 −21 0.071 12 Example 3-25,710 0.062 16 −22 0.072 14 Example 3-7 5,700 0.061 14 −20 0.071 12

TABLE 3-5 Load at 125° C. Initial characteristics for 1,000 hr Cap tan δLC ΔCap tan δ LC Example 3-1 5,700 0.061 15 −23 0.076 32 Example 3-25,700 0.062 18 −22 0.074 41 Example 37 5,690 0.061 14 −21 0.075 29

As it is understood from Tables 3-2 to 3-5, the service lifecharacteristics at 105° C. and 125° C. after 1,000 hours of the Exampleswere excellent. The capacitance in the initial stage is also high. Incomparison to these, Comparative Examples 3-1 and 3-2 having onlydiammonium hydrogenphosphate added suffer from opening of the valve eventhough 0.005 part and 1 part, respectively, of diammoniumhydrogenphosphate are added to the electrolytic solutions, and theleakage current in the initial stage is high in Comparative Example 3-2having 1 part of diammonium hydrogenphosphate added.

Furthermore, Comparative Example 3-3 having neither chelating agent nordiammonium hydrogenphosphate added has a specific resistance of 80 and atan δ of from 0.109 to 0.110, which are in the lowest level as theconventional products, but suffers from opening of the valve, andtherefore, it is understood that the invention realizes an electrolyticcapacitor, which has low tan δ characteristics that are notconventionally attained and has good high-temperature service lifecharacteristics.

Advantage of the Invention:

The phosphoric acid compound and the chelating agent are added to thesolvent containing water as a main component in the electrolyticsolution for an electrolytic capacitor in the invention, and therefore,the content of water can be increased to 100% by weight of the solvent,so as to obtain a high electroconductivity of the electrolytic solution.Furthermore, blister and opening of the valve of the capacitor areprevented, and the tan δ characteristics after the high-temperature testand the leakage current characteristics after the high-temperature noload test are also improved. As described in the foregoing, anelectrolytic capacitor having impedance characteristics andhigh-temperature service life characteristics that are notconventionally attained, and improved shelf characteristics can berealized owing to the synergistic effect among the solvent containingwater as a main component, the phosphoric acid compound and thechelating agent in the electrolytic solution for an electrolyticcapacitor of the invention.

What is claimed is:
 1. An electrolytic solution for an aluminum electrolytic capacitor containing a solvent containing water in an amount of 35 to 100% by weight of the entire solvent and a water-soluble aluminum complex having a phosphate ion combined thereto.
 2. An electrolytic solution for an aluminum electrolytic capacitor according to claim 1, wherein said solvent contains water as a main component.
 3. An electrolytic solution for an aluminum electrolytic capacitor according to claim 1, wherein said water-soluble aluminum complex having a phosphate ion combined thereto is formed by adding a compound forming a phosphate ion in an aqueous solution and a chelating agent forming a water-soluble aluminum complex with aluminum.
 4. An electrolytic solution for an aluminum electrolytic capacitor according to claim 3, wherein said compound forming a phosphate ion in an aqueous solution is at least one kind selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid or salts thereof; a phosphate or an alkylphosphate, a phosphonate, a diphosphonate or a derivative thereof, a phosphinate, or a salt thereof; and a condensate thereof or a salt of said condensate.
 5. An electrolytic solution for an aluminum electrolytic capacitor according to claim 1, wherein at least one kind of adipic acid and a salt thereof is used as a solute.
 6. An electrolytic solution for an aluminum electrolytic capacitor according to claim 5, wherein a content of adipic acid or a salt thereof is from 5 to 20% by weight of the entire electrolytic solution.
 7. An electrolytic solution for an aluminum electrolytic capacitor according to claim 3, wherein a content of said compound forming a phosphate ion in an aqueous solution is from 0.01 to 3.0% by weight of the entire electrolytic solution.
 8. An electrolytic solution for an aluminum electrolytic capacitor according to claim 3, wherein a content of said chelating agent is from 0.01 to 3.0% by weight of the entire electrolytic solution.
 9. An electrolytic solution for an aluminum electrolytic capacitor according to claim 3, wherein said chelating agent is at least one kind selected from the group consisting of citric acid, tartaric acid, gluconic acid, malic acid, lactic acid, glycolic acid, α-hydroxybutylic acid, hydroxymalonic acid, α-methylmalic acid, dihydroxytartaric acid, γ-resocylic acid, β-resocylic acid, trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid, phenoltricarboxylic acid, aluminon, Eriochrome Cyanine R, sulfosalicylic acid, tannic acid, dicyandiamide, galactose, glucose, lignosulfonate, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), glycoletherdiaminetetraacetic acid (GEDTA), di-ethylenetriaminepentaacetic acid (DTPA), hydroxyethyl-ethylenediaminetriacetic acid (HEDTA), triethylene-tetraminehexaacetic acid (TTHA), and salts of them. 